Occupant position and weight estimation systems are useful in connection with air bags and other pyrotechnically deployed restraints for purposes of determining whether, and how forcefully, to deploy the restraints. For example, deployment of an air bag can be disabled if the occupant is positioned in close proximity to the air bag cover, or if the seated weight of the occupant is indicative of an infant seat or a small child. A well known weight estimation technique is to locate a fluid-filled bladder in or under a vehicle seat cushion, and to estimate the seated weight of the occupant based on the fluid pressure in the bladder. See for example, the U.S. Pat. Nos. 5,987,370 and 6,246,936 to Murphy et al., the U.S. Pat. Nos. 6,101,436 and 6,490,936 to Fortune et al., and in particular the U.S. Pat. No. 6,578,871 to Gray et al. which discloses the use of a seat bladder having multiple fluid-filled chambers corresponding to different areas of the seat cushion. In Gray et al., fluid pressures in the various chambers of the bladder are individually measured and summed to form a composite pressure, and the composite pressure is adjusted in a direction to favor restraint enablement when the pressure in an outboard chamber of the bladder significantly exceeds the average pressure. On the other hand, the restraints are disabled if the pressure distribution indicates that the occupant is positioned at the front of the seat cushion in close proximity to the air bag cover.
In a production vehicle, the capabilities of occupant position and weight estimation systems are typically limited due to cost considerations, and the systems are ideally designed to acquire the necessary information about the occupant while minimizing system cost. For example, a seat bladder can be used to reliably characterize an occupant with relatively low system cost, but the use of a bladder with several chambers and individual pressure sensors may be cost prohibitive in many vehicles. Accordingly, what is needed is way of maximizing the occupant information available from a low-cost position and weight estimation system.